linux-kernel - Re: [PATCH 01/16] PCI/P2PDMA: Pass gfp_mask flags to upstream_bridge_distance

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Message-ID: <c078b970-7531-8834-e26f-e653e7db4c20@redhat.com>
Date:   Tue, 11 May 2021 12:23:10 -0400
From:   Don Dutile <ddutile@...hat.com>
To:     Logan Gunthorpe <logang@...tatee.com>,
        John Hubbard <jhubbard@...dia.com>,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-block@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org
Cc:     Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian König <christian.koenig@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jakowski Andrzej <andrzej.jakowski@...el.com>,
        Minturn Dave B <dave.b.minturn@...el.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Jianxin <jianxin.xiong@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH 01/16] PCI/P2PDMA: Pass gfp_mask flags to
 upstream_bridge_distance_warn()

On 5/11/21 12:12 PM, Logan Gunthorpe wrote:
>
> On 2021-05-11 10:05 a.m., Don Dutile wrote:
>> On 5/1/21 11:58 PM, John Hubbard wrote:
>>> On 4/8/21 10:01 AM, Logan Gunthorpe wrote:
>>>> In order to call upstream_bridge_distance_warn() from a dma_map function,
>>>> it must not sleep. The only reason it does sleep is to allocate the seqbuf
>>>> to print which devices are within the ACS path.
>>>>
>>>> Switch the kmalloc call to use a passed in gfp_mask and don't print that
>>>> message if the buffer fails to be allocated.
>>>>
>>>> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
>>>> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
>>>> ---
>>>>    drivers/pci/p2pdma.c | 21 +++++++++++----------
>>>>    1 file changed, 11 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
>>>> index 196382630363..bd89437faf06 100644
>>>> --- a/drivers/pci/p2pdma.c
>>>> +++ b/drivers/pci/p2pdma.c
>>>> @@ -267,7 +267,7 @@ static int pci_bridge_has_acs_redir(struct pci_dev *pdev)
>>>>      static void seq_buf_print_bus_devfn(struct seq_buf *buf, struct pci_dev *pdev)
>>>>    {
>>>> -    if (!buf)
>>>> +    if (!buf || !buf->buffer)
>>> This is not great, sort of from an overall design point of view, even though
>>> it makes the rest of the patch work. See below for other ideas, that will
>>> avoid the need for this sort of odd point fix.
>>>
>> +1.
>> In fact, I didn't see how the kmalloc was changed... you refactored the code to pass-in the
>> GFP_KERNEL that was originally hard-coded into upstream_bridge_distance_warn();
>> I don't see how that avoided the kmalloc() call.
>> in fact, I also see you lost a failed kmalloc() check, so it seems to have taken a step back.
> I've changed this in v2 to just use some memory allocated on the stack.
> Avoids this argument all together.
>
> Logan
>
Looking fwd to the v2; again, my apologies for the delay, and the redundancy it's adding to your feedback review & changes.
-Don